Column base assembly

ABSTRACT

A column baseplate assembly utilizing dowel members to absorb concentric loading as well as shear or moment. The dowel members transfer the stresses along substantially their entire length permitting the use of a much smaller baseplate.

United States Patent Schweinberger Nov. 11, 1975 [5 COLUMN BASE ASSEMBLY3,540,177 11/1970 Slining 52/295 x 3,568,380 3/1971 Stuch [76] Inventor:Manfred schwemberger 407 N 3,653,169 4/1972 J6me: 52/296 x 6299 SeattleWash- 98103 3,671,738 6/1972 Beachley 52/296 x 22] Filed: 2 1 3,733,7575/1973 Scott 52/296 X [211 App. No; 473,419 FOREIGN PATENTS ORAPPLICATIONS 1,044,365 11/1953 France 52/403 52] us. c1. 52/295; 52/296;52/403 OTHER. PUBLICATIONS [51] Int. Cl. E02D 27/42 Acier Stahl Steelntr May, 63, p- 09- [58] Field of Search 52/294, 296, 295, 297,

52/ 334, 733, 403 Prinmry E.\'aminerEmest R. Purser AssistantE.\'aminerLeslie A. Braun [56] References Cited Attorney, Agent, orFI'rmSeed, Berry, Vernon &

UNITED STATES PATENTS Baynham 889,240 6/1908 Kanski 52/403 1,585,2545/1926 Lund et a1. 52/295 x [57] ABSTRACT 2,724,261 1 H1955 Rensaa52/295 A Column baseplate assembly utilizing dowel members 2,899,7718/1959 Burris, Jr, 52/517 X to absorb concentric loading as well asshear or me- 2,952,938 9/1960 Abrams 52/5l7 ment. The dowel memberstransfer the stresses along 3 28? substantially their entire lengthpermitting the use of a 0C a ran et a 3,374,592 3/1968 Cheskin 52/733 xmuch smaller baseplate' 3,473,285 10/1969 Reitand 52/295 x 6 Claims, 2Drawing Figures COLUMN BASE ASSEMBLY BACKGROUND OF THE INVENTION Thisinvention relates to a baseplate assembly which affects transfer ofaxial loads, shear forces and bending moments from a metal column orother structural member to the supporting concrete structure, caisson orfooting with substantially greater reliability and efficiency than theconventional baseplate with anchor bolts can achieve.

The concentration of stresses into a smaller area results in a moreeconomical baseplate of high strength steel and savings in theimmediately adjacent parts of the structure. This is especially true forheavy loads, such as accumulate in columns of high rise buildings,industrial structures, supports of bridges and equipment or the like.

The capability of the baseplate assembly to transfer forces induced byearthquake or wind to the supporting concrete structure, footing orcaisson is an'attribute which lately has received increased recognitionas to its importance by the niform Building Code, published by theInternational Conference of Building Officials and is a factorconsidered critical by insurance underwriters. A

Outstanding features of this invention in comparison to the conventionalbaseplate with anchor bolts are, that this assembly is completely shopfabricated, designed to accommodate a desired load, shear and momentcapacity and can be installed in one simple operation. i

The adaptability of the assembly to special column shapes and restrictedconditions is a valuable cost saving and convenient aspectdistinguishing the assembly from prior art structures. Rigid framestructures benefit substantially from this very effective way of tyingthe framework to the concrete base structure or foundation.

With reference to the accompanying description and drawing it becomesapparent, thata greatvariety of arrangements are possible within thescope of the present invention enabling the designer toiachieve the mosteffective and suitable assembly for any particular local requirementwith relative ease and economy. A listing of baseplate assemblies foruse with standard rolled column sections and the most common load rangescan be prepared for easy selection, ordering and fabrication. A computerprogram can also be made available to cover all general and specialconditions for quick and accurate design and detailing of baseplateassemblies.

BRIEF DESCRIPTION OF THE DRAWINGS- FIG. 1 is a top plan view of theinventive baseplate assembly.

FIG. 2 is a vertical section taken along line 2-2 in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS As seen in the FIGS., the inventivebaseplate assem in concrete l5 and may further include bar ties 14 asrequired by the building code or alternatively spiral reinforcing toretard the possibility of breakage of the concrete envelope 15 in theevent of a predicted bending moment or shear force. A membrane 16 is isplaced below the baseplate 12 to allow vertical compression of thereinforcing bars 13 without over stressing the concrete caused bydifferential shortening of the dowels 13.

The column 11 or any member supported by, but not part of the baseplateassembly becomes an integral part of the assembly, when field welded orotherwise joined to the top of the baseplate 12. In FIGS. 1 and 2 thecolumn 11 is indicated in phantom, not being a part of the presentinvention, and is shown as, but not limited to a standard rolled steelsection. Any shape or size of metal column or other member may beaccommodated, however, and it is important to choose the mostappropriate shape for the baseplate l2 and to determine the bestarrangement and placement of the reinforcing bar dowels 13 below thebaseplate 12. The dowels will be placed to take advantage of thestiffening effect this member or column 11 has on the baseplate 12.

The use of high strength steel for the baseplate 12, up to four inchesin thickness is made possible by closely spaced reinforcing bar dowels13 of at least 60,000 pounds per square inch yield strength and with alength necessary to transmit their design load capacity through bond tothe supporting concrete 15 along substantially the entire length. Therelatively large portion of load that transfers from the baseplate 12 tothe dowels 13 directly is gradually dissipated to the supportingconcrete 15 below and thereby avoids a concentration of stressimmediately under the baseplate 12. It is critical that this load not bein excess of that permitted by code.

The number of reinforcing bar dowels 13 required is determined byultimate strength design method for short columns for the portion ofload not transferred to the supporting concrete 15 by direct bearingunder the baseplate 12. Alternate to reinforcing bar dowels 13, steelbars or metal shapes with bond and stress qualities equal or superior tothose of the reinforcing bar dowels l3 mentioned above, capable of beingattached to the baseplate 12 in a manner similar to the studweld method,will greatly facilitate manufacture of the assembly. When required bybuilding codes closely spaced reinforcing bar ties 14 or spirals for theportion of concrete l5 enveloping said dowels l3 assure ductility of theconcrete especially when large bending moments are to be accommodated.

The need for ties 14 or spirals are only nominal if ductility is assuredthrough adequate reinforcing of the supporting concrete structure 15 incompliance with the requirements of the building code.

In applying these assumptions to the design of the assembly it becomesof greatest importance to avoid stress concentrations in the concrete 15immediately beneath the baseplate 12. A thin membrane 16 of lowcompressible strength is attached to the entire underside of thebaseplate 12, except where, the reinforcing bar dowels 13 are welded.The thickness of this membrane 16 is determined by the amount ofdifferential shortening taking place in the reinforcing bar dowels 13and the enveloping concrete 15 as loads are applied to the assembly. Allvalues necessary for establishing the membrane thickness are readilyavailable. Bond length requirements for the reinforcing bar dowels l3and the modulus of the elasticity for the various strengths concrete 15are available from any one of a number of publications by the AmericanConcrete Institute. The modulus of elasticity for a typical reinforcingbar dowel is 29 X psi. The load applied to the dowel l3 dissipatesthrough uniform bond stresses along their entire length to theenveloping concrete.

This method of calculation makes certain that the reinforcing bar dowels13 are loaded to their design capacity and that the membrane 16compresses before the portion of load that transfers from the baseplate12 to the concrete directly, does not exceed stress limitations requiredby code. In order to meet the code required stress limitations themembrane must satisfy two requirements. First it must permit thereinforcing bar dowels to fully develop their compressive stresscapacity and the accompanying elastic shortening. Secondly the membrane,while undergoing a thickness change equal to the elastic shortening ofthe rebar dowels, must develop compression stresses no greater thanthose permitted by code for the adjacent concrete. Many availablematerials such as styrofoam, paper, rubber and cloth of predictableconsistency, thickness and performance when subjected to compressiveforces can be used to adequately fulfill the requirements for theaforementioned membrane. As a general statement of the requirements ofthe membrane are that it passes the quality or characteristics of havingless compression resistance and more elasticity than the supportingconcrete upon which the membrane is positioned between the baseplate.

The 4 inch maximum thickness requirement for high strength steelbaseplates 12 may in some instances also necessitate welding on ofstiffener plates or the use of a baseplate built up from a combinationof plates and- /or rolled shapes to satisfy stress limitations. Thestiffener plates may be welded to the top side of the baseplate 12 incombination with the column 11 unless the dual purpose of transmittingshear can be better served by welding the stiffener plates to the bottomside.

The hereinabove mentioned method of design and installation of theassembly avoids overstressing the concrete 15 or metal parts beyondvalues permitted by applicable codes or substantiated by test results.Development of a computer analysis in connection with a test program mayresult in a more economical baseplate assembly than can be realizedwithin the present code limitations.

The use of this baseplate assembly offers considerable advantages overthe conventional baseplate with anchor bolts. For heavily loaded columnsa drastic reduction in steel tonnage can be realized. The top of thebaseplate can be placed very close to the floor, thus shortening thecolumn length. The assembly is relatively small in plan area and can beplaced directly into the top of a caisson, concrete members or piers,eliminating the need for a concrete cap and anchor bolts. Uplift, shearand moment capacity as desired can be accommodated at little or no extracost, a very important attribute for the frame structures, bridge andcolumn supports, etc., in earthquake areas and high wind zones.

It is to be understood that although the present invention has beenparticularly described with reference to a vertical column. theprinciples are equally applicable to the securement of any elongatedmember subject to analogous stresses.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A column supporting assembly adapted to support a structural loadbearing column or the like capable of withstanding vertical loads, shearforces and moment, said column supporting assembly comprising a flatrelatively thick steel baseplate, said baseplate including a top, columnsupporting surface and a bottom surface, a plurality of steelreinforcing rods of substantial length rigidly connected in fixedposition to said bottom surface and extending downwardly from saidbottom surface substantially normal to said bottom surface of saidbaseplate, a concrete mass having a top surface area at least equal tothe area of said baseplate surrounding said rods and extending below thelower ends of said rods, a relatively thin compressible membranepositioned between the bottom surface of said baseplate and the topsurface of said concrete mass whereby forces exerted on said column aretransmitted through said baseplate to said rods and the membrane iscompressed prior to the forces being exerted on said concrete and asubstantial portion of the initial force that transfers through saidbaseplate is gradually dissipated to the supporting concrete adjacentsaid rods thereby avoiding a concentration of the initial force on theconcrete immediately underlying said baseplate and said membrane beingformed from substances having a property of being less compressionresistant and greater elasticity than the supporting concrete upon whichthe membrane is positioned.

2. A column assembly as in claim 1 wherein said membrane is formed fromstyrofoam.

3. A column assembly as in claim 1 wherein said membrane is formed frompaper.

4. A column assembly as in claim 1 wherein said membrane is formed fromrubber.

5. A column assembly as in claim 1 wherein said membrane is formed fromcloth.

6. A column supporting assembly as in claim 1 wherein said steelreinforcing rods are interconnected by steel tie members at verticallyspaced positions along the length of said reinforcing rods.

1. A column supporting assembly adapted to support a structural loadbearing column or the like capable of withstanding vertical loads, shearforces and moment, said column supporting assembly comprising a flatrelatively thick steel baseplate, said baseplate including a top, columnsupporting surface and a bottom surface, a plurality of steelreinforcing rods of substantial length rigidly connected in fixedposition to said bottom surface and extending downwardly from saidbottom surface substantially normal to said bottom surface of saidbaseplate, a concrete mass having a top surface area at least equal tothe area of said baseplate surrounding said rods and extending Below thelower ends of said rods, a relatively thin compressible membranepositioned between the bottom surface of said baseplate and the topsurface of said concrete mass whereby forces exerted on said column aretransmitted through said baseplate to said rods and the membrane iscompressed prior to the forces being exerted on said concrete and asubstantial portion of the initial force that transfers through saidbaseplate is gradually dissipated to the supporting concrete adjacentsaid rods thereby avoiding a concentration of the initial force on theconcrete immediately underlying said baseplate and said membrane beingformed from substances having a property of being less compressionresistant and greater elasticity than the supporting concrete upon whichthe membrane is positioned.
 2. A column assembly as in claim 1 whereinsaid membrane is formed from styrofoam.
 3. A column assembly as in claim1 wherein said membrane is formed from paper.
 4. A column assembly as inclaim 1 wherein said membrane is formed from rubber.
 5. A columnassembly as in claim 1 wherein said membrane is formed from cloth.
 6. Acolumn supporting assembly as in claim 1 wherein said steel reinforcingrods are interconnected by steel tie members at vertically spacedpositions along the length of said reinforcing rods.